Film formation method and apparatus for semiconductor process

ABSTRACT

A silicon nitride film is formed on a target substrate by performing a plurality of cycles in a process field configured to be selectively supplied with a first process gas containing a silane family gas and a second process gas containing a nitriding gas. Each of the cycles includes a first supply step of performing supply of the first process gas while maintaining a shut-off state of supply of the second process gas, and a second supply step of performing supply of the second process gas, while maintaining a shut-off state of supply of the first process gas. The method is arranged to repeat a first cycle set with the second supply step including an excitation period of exciting the second process gas and a second cycle set with the second supply step including no period of exciting the second process gas.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a film formation method and apparatusfor a semiconductor process for forming a silicon nitride film on atarget substrate, such as a semiconductor wafer. The term “semiconductorprocess” used herein includes various kinds of processes which areperformed to manufacture a semiconductor device or a structure havingwiring layers, electrodes, and the like to be connected to asemiconductor device, on a target substrate, such as a semiconductorwafer or a glass substrate used for an FPD (Flat Panel Display), e.g.,an LCD (Liquid Crystal Display), by forming semiconductor layers,insulating layers, and conductive layers in predetermined patterns onthe target substrate.

2. Description of the Related Art

In manufacturing semiconductor devices for constituting semiconductorintegrated circuits, a target substrate, such as a semiconductor wafer,is subjected to various processes, such as film formation, etching,oxidation, diffusion, reformation, annealing, and natural oxide filmremoval. US 2006/0286817 A1 discloses a semiconductor processing methodof this kind performed in a vertical heat-processing apparatus (of theso-called batch type). According to this method, semiconductor wafersare first transferred from a wafer cassette onto a vertical wafer boatand supported thereon at intervals in the vertical direction. The wafercassette can store, e.g., 25 wafers, while the wafer boat can support 30to 150 wafers. Then, the wafer boat is loaded into a process containerfrom below, and the process container is airtightly closed. Then, apredetermined heat process is performed, while the process conditions,such as process gas flow rate, process pressure, and processtemperature, are controlled.

In order to improve the performance of semiconductor integratedcircuits, it is important to improve properties of insulating films usedin semiconductor devices. Semiconductor devices include insulating filmsmade of materials, such as SiO₂, PSG (Phospho Silicate Glass), P—SiO(formed by plasma CVD), P—Si—N (formed by plasma CVD), and SOG (Spin OnGlass), Si₃N₄ (silicon nitride). Particularly, silicon nitride films arewidely used, because they have better insulation properties as comparedto silicon oxide films, and they can sufficiently serve as etchingstopper films or inter-level insulating films. Further, for the samereason, carbon nitride films doped with boron are sometimes used.

Several methods are known for forming a silicon nitride film on thesurface of a semiconductor wafer by thermal CVD (Chemical VaporDeposition). In such thermal CVD, a silane family gas, such asmonosilane (SiH₄), dichlorosilane (DCS: SiH₂Cl₂), hexachlorodisilane(HCD: Si₂Cl₆), bistertialbutylaminosilane (BTBAS: SiH₂(NH(C₄H₉))₂), or(t-C₄H₉NH)₂SiH₂, is used as a silicon source gas. For example, a siliconnitride film is formed by thermal CVD using a gas combination ofSiH₂Cl₂+NH₃ (see U.S. Pat. No. 5,874,368 A) or Si₂Cl₆+NH₃. Further,there is also proposed a method for doping a silicon nitride film withan impurity, such as boron (B), to decrease the dielectric constant.

In recent years, owing to the demands of increased miniaturization andintegration of semiconductor integrated circuits, it is required toalleviate the thermal history of semiconductor devices in manufacturingsteps, thereby improving the characteristics of the devices. Forvertical processing apparatuses, it is also required to improvesemiconductor processing methods in accordance with the demandsdescribed above. For example, there is a CVD (Chemical Vapor Deposition)method for a film formation process, which performs film formation whileintermittently supplying a source gas and so forth to repeatedly formlayers each having an atomic or molecular level thickness, one by one,or several by several (for example, Jpn. Pat. Appln. KOKAI PublicationsNo. 2-93071 and No. 6-45256 and U.S. Pat. No. 6,165,916 A). In general,this film formation method is called ALD (Atomic layer Deposition) orMLD (Molecular Layer Deposition), which allows a predetermined processto be performed without exposing wafers to a very high temperature.

For example, where dichlorosilane (DCS) and NH₃ are supplied as a silanefamily gas and a nitriding gas, respectively, to form a silicon nitridefilm (SiN), the process is performed, as follows. Specifically, DCS andNH₃ gas are alternately and intermittently supplied into a processcontainer with purge periods interposed therebetween. When NH₃ gas issupplied, an RF (radio frequency) is applied to generate plasma withinthe process container so as to promote a nitridation reaction. Morespecifically, when DCS is supplied into the process container, a layerwith a thickness of one molecule or more of DCS is adsorbed onto thesurface of wafers. The superfluous DCS is removed during the purgeperiod. Then, NH₃ is supplied and plasma is generated, therebyperforming low temperature nitridation to form a silicon nitride film.These sequential steps are repeated to complete a film having apredetermined thickness.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a film formation methodand apparatus for a semiconductor process, which can form a siliconnitride film of high quality at a high film formation rate whilepreventing particle generation.

According to a first aspect of the present invention, there is provideda film formation method for a semiconductor process for forming asilicon nitride film on a target substrate, in a process field inside aprocess container configured to be selectively supplied with a firstprocess gas containing a silane family gas and a second process gascontaining a nitriding gas, and communicating with an exciting mechanismfor exciting the second process gas to be supplied, the methodcomprising a film formation process arranged to perform a plurality ofcycles in the process field with the target substrate placed therein tolaminate thin films respectively formed by the cycles on the targetsubstrate, thereby forming a silicon nitride film with a predeterminedthickness, each of the cycles comprising: a first supply step ofperforming supply of the first process gas to the process field whilemaintaining a shut-off state of supply of the second process gas to theprocess field; and a second supply step of performing supply of thesecond process gas to the process field while maintaining a shut-offstate of supply of the first process gas to the process field, whereinthe method is arranged to repeat a first cycle set and a second cycleset mixedly a plurality of times without an essential change in aheating temperature set to the process field: the first cycle set beingcomposed of a cycle or cycles in which the second supply step comprisesan excitation period of supplying the second process gas to the processfield while exciting the second process gas by the exciting mechanism;and the second cycle set being composed of a cycle or cycles in whichthe second supply step comprises no period of exciting the secondprocess gas by the exciting mechanism.

According to a second aspect of the present invention, there is provideda film formation apparatus for a semiconductor process, comprising: aprocess container having a process field configured to accommodate atarget substrate; a support member configured to support the targetsubstrate inside the process field; a heater configured to heat thetarget substrate inside the process field; an exhaust system configuredto exhaust gas from the process field; a first process gas supplycircuit configured to supply a first process gas containing a silanefamily gas to the process field; a second process gas supply circuitconfigured to supply a second process gas containing a nitriding gas tothe process field; an exciting mechanism configured to excite the secondprocess gas to be supplied; and a control section configured to controlan operation of the apparatus, wherein the control section is preset toexecute a film formation method for a semiconductor process for forminga silicon nitride film on the target substrate, the method comprising afilm formation process arranged to perform a plurality of cycles in theprocess field with the target substrate placed therein to laminate thinfilms respectively formed by the cycles on the target substrate, therebyforming a silicon nitride film with a predetermined thickness, each ofthe cycles comprising: a first supply step of performing supply of thefirst process gas to the process field while maintaining a shut-offstate of supply of the second process gas to the process field; and asecond supply step of performing supply of the second process gas to theprocess field while maintaining a shut-off state of supply of the firstprocess gas to the process field, wherein the method is arranged torepeat a first cycle set and a second cycle set mixedly a plurality oftimes without an essential change in a heating temperature set to theprocess field: the first cycle set being composed of a cycle or cyclesin which the second supply step comprises an excitation period ofsupplying the second process gas to the process field while exciting thesecond process gas by the exciting mechanism; and the second cycle setbeing composed of a cycle or cycles in which the second supply stepcomprises no period of exciting the second process gas by the excitingmechanism.

According to a third aspect of the present invention, there is provideda computer readable medium containing program instructions for executionon a processor, which is used for a film formation apparatus for asemiconductor process for forming a silicon nitride film on a targetsubstrate, in a process field inside a process container configured tobe selectively supplied with a first process gas containing a silanefamily gas and a second process gas containing a nitriding gas, andcommunicating with an exciting mechanism for exciting the second processgas to be supplied, wherein the program instructions, when executed bythe processor, cause the film formation apparatus to conduct a filmformation method comprising a film formation process arranged to performa plurality of cycles in the process field with the target substrateplaced therein to laminate thin films respectively formed by the cycleson the target substrate, thereby forming a silicon nitride film with apredetermined thickness, each of the cycles comprising: a first supplystep of performing supply of the first process gas to the process fieldwhile maintaining a shut-off state of supply of the second process gasto the process field; and a second supply step of performing supply ofthe second process gas to the process field while maintaining a shut-offstate of supply of the first process gas to the process field, whereinthe method is arranged to repeat a first cycle set and a second cycleset mixedly a plurality of times without an essential change in aheating temperature set to the process field: the first cycle set beingcomposed of a cycle or cycles in which the second supply step comprisesan excitation period of supplying the second process gas to the processfield while exciting the second process gas by the exciting mechanism;and the second cycle set being composed of a cycle or cycles in whichthe second supply step comprises no period of exciting the secondprocess gas by the exciting mechanism.

In the first to third aspects, before forming the silicon nitride filmon the target substrate, the method may further comprise a pre-coatingprocess arranged to perform a plurality of pre-cycles in the processcontainer with no target substrate placed therein to form a pre-coatingfilm inside the process container, each of the pre-cycles comprising: afirst pre-step of performing supply of the first process gas into theprocess container while maintaining a shut-off state of supply of thesecond process gas into the process container; and a second pre-step ofperforming supply of the second process gas into the process containerwhile maintaining a shut-off state of supply of the first process gasinto the process container, wherein the second pre-step comprises noperiod of exciting the second process gas by the exciting mechanism.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention, andtogether with the general description given above and the detaileddescription of the embodiments given below, serve to explain theprinciples of the invention.

FIG. 1 is a sectional view showing a film formation apparatus (verticalCVD apparatus) according to an embodiment of the present invention;

FIG. 2 is a sectional plan view showing part of the apparatus shown inFIG. 1;

FIG. 3 is a timing chart showing the gas supply and RF (radio frequency)application of a film formation method according to an embodiment of thepresent invention;

FIG. 4 is a view showing a modification concerning the ON-state of an RFpower supply in the NH₃ gas supply step;

FIG. 5 is a sectional view showing the laminated state of a siliconnitride film formed by use of the timing chart shown in FIG. 3;

FIG. 6 is a diagram showing combinations of cycle sets performed withplasma and cycle sets performed without plasma, according to presentexamples and comparative examples used in an experiment;

FIG. 7 is a graph showing particle generation, in association withsilicon nitride films formed by the present examples and comparativeexamples shown in FIG. 6;

FIG. 8 is a graph showing the stress of silicon nitride films formed bythe present examples and comparative examples shown in FIG. 6;

FIG. 9 is a graph showing the film formation rate and theinter-substrate uniformity and planar uniformity of the film thickness,in association with silicon nitride films formed by the present examplesand comparative examples shown in FIG. 6;

FIG. 10 is a graph showing the etching rate of silicon nitride filmsformed by the present examples and comparative examples shown in FIG. 6;and

FIGS. 11A and 11B are timing charts each showing the gas supply and RF(radio frequency) application of a film formation method according to amodification of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the process of developing the present invention, the inventorsstudied problems of conventional techniques for semiconductor processes,in relation to methods for forming a silicon nitride film. As a result,the inventors have arrived at the findings given below.

Specifically, as described previously, there is a conventional techniquearranged to utilize so-called ALD or MLD film formation and to generateplasma by use of radio frequency (RF) when supplying NH₃ gas as anitriding gas, thereby promoting the nitridation reaction. As comparedto a process performed without plasma, this process can improve not onlythe film formation rate (film formation speed), but also the quality ofthe deposited silicon nitride film to a large extent. However, it hasbeen confirmed that, where plasma generation is used, particlegeneration inside the process container is increased due to an increasein the stress of the deposited silicon nitride film and so forth.

In this respect, it has been found that, where ALD or MLD film formationis performed such that cycle sets excluding plasma generation insupplying a nitriding gas are mixed with cycle sets including plasmageneration in supplying a nitriding gas, the particle generation can besuppressed. Accordingly, where a suitable mixture manner of cycle setsis selected in accordance with this concept, a silicon nitride film ofhigh quality can be formed at a high film formation rate whilepreventing particle generation. In addition, where a pre-coating processis performed inside the process container by use of cycle sets excludingplasma generation in supplying a nitriding gas, before the filmformation process, the effect described above is further improved.

An embodiment of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be made only when necessary.

FIG. 1 is a sectional view showing a film formation apparatus (verticalCVD apparatus) according to an embodiment of the present invention. FIG.2 is a sectional plan view showing part of the apparatus shown inFIG. 1. The film formation apparatus 2 has a process field configured tobe selectively supplied with a first process gas containingdichlorosilane (DCS) gas as a silane family gas, and a second processgas containing ammonia (NH₃) gas as a nitriding gas. The film formationapparatus 2 is configured to form a silicon nitride film on targetsubstrates in the process field.

The apparatus 2 includes a process container 4 shaped as a cylindricalcolumn with a ceiling and an opened bottom, in which a process field 5is defined to accommodate and process a plurality of semiconductorwafers (target substrates) stacked at intervals in the verticaldirection. The entirety of the process container 4 is made of, e.g.,quartz. The top of the process container 4 is provided with a quartzceiling plate 6 to airtightly seal the top. The bottom of the processcontainer 4 is connected through a seal member 10, such as an O-ring, toa cylindrical manifold 8. The process container may be entirely formedof a cylindrical quartz column without a manifold 8 separately formed.

The manifold 8 is made of, e.g., stainless steel, and supports thebottom of the process container 4. A wafer boat 12 made of quartz ismoved up and down through the bottom port of the manifold 8, so that thewafer boat 12 is loaded/unloaded into and from the process container 4.A number of target substrates or semiconductor wafers W are stacked on awafer boat 12. For example, in this embodiment, the wafer boat 12 hasstruts 12A that can support, e.g., about 50 to 100 wafers having adiameter of 300 mm at essentially regular intervals in the verticaldirection.

The wafer boat 12 is placed on a table 16 through a heat-insulatingcylinder 14 made of quartz. The table 16 is supported by a rotary shaft20, which penetrates a lid 18 made of, e.g., stainless steel, and isused for opening/closing the bottom port of the manifold 8.

The portion of the lid 18 where the rotary shaft 20 penetrates isprovided with, e.g., a magnetic-fluid seal 22, so that the rotary shaft20 is rotatably supported in an airtightly sealed state. A seal member24, such as an O-ring, is interposed between the periphery of the lid 18and the bottom of the manifold 8, so that the interior of the processcontainer 4 can be kept sealed.

The rotary shaft 20 is attached at the distal end of an arm 26 supportedby an elevating mechanism 25, such as a boat elevator. The elevatingmechanism 25 moves the wafer boat 12 and lid 18 up and downintegratedly. The table 16 may be fixed to the lid 18, so that wafers Ware processed without rotation of the wafer boat 12.

A gas supply section is connected to the side of the manifold 8 tosupply predetermined process gases to the process field 5 within theprocess container 4. Specifically, the gas supply section includes asecond process gas supply circuit 28, a first process gas supply circuit30, and a purge gas supply circuit 36. The first process gas supplycircuit 30 is arranged to supply a first process gas containing a silanefamily gas, such as DCS (dichlorosilane) gas. The second process gassupply circuit 28 is arranged to supply a second process gas containinga nitriding gas, such as ammonia (NH₃) gas. The purge gas supply circuit36 is arranged to supply an inactive gas, such as N₂ gas, as a purgegas. Each of the first and second process gases is mixed with a suitableamount of carrier gas, as needed. However, such a carrier gas will notbe mentioned, hereinafter, for the sake of simplicity of explanation.

More specifically, the second and first process gas supply circuits 28and 30 include gas distribution nozzles 38 and 40, respectively, each ofwhich is formed of a quartz pipe which penetrates the sidewall of themanifold 8 from the outside and then turns and extends upward (see FIG.1). The gas distribution nozzles 38 and 40 respectively have a pluralityof gas spouting holes 38A and 40A, each set of holes being formed atpredetermined intervals in the longitudinal direction (the verticaldirection) over all the wafers W on the wafer boat 12. Each of the gasspouting holes 38A and 40A delivers the corresponding process gas almostuniformly in the horizontal direction, so as to form gas flows parallelwith the wafers W on the wafer boat 12. The purge gas supply circuit 36includes a short gas nozzle 46, which penetrates the sidewall of themanifold 8 from the outside.

The nozzles 38, 40, and 46 are connected to gas sources 28S, 30S, and36S of NH₃ gas, DCS gas, and N₂ gas, respectively, through gas supplylines (gas passages) 48, 50, and 56, respectively. The gas supply lines48, 50, and 56 are provided with switching valves 48A, 50A, and 56A andflow rate controllers 48B, 50B, and 56B, such as mass flow controllers,respectively. With this arrangement, NH₃ gas, DCS gas, and N₂ gas can besupplied at controlled flow rates.

A gas exciting section 66 is formed at the sidewall of the processcontainer 4 in the vertical direction. On the side of the processcontainer 4 opposite to the gas exciting section 66, a long and thinexhaust port 68 for vacuum-exhausting the inner atmosphere is formed bycutting the sidewall of the process container 4 in, e.g., the verticaldirection.

Specifically, the gas exciting section 66 has a vertically long and thinopening 70 formed by cutting a predetermined width of the sidewall ofthe process container 4, in the vertical direction. The opening 70 iscovered with a quartz cover 72 airtightly connected to the outer surfaceof the process container 4 by welding. The cover 72 has a vertical longand thin shape with a concave cross-section, so that it projects outwardfrom the process container 4.

With this arrangement, the gas exciting section 66 is formed such thatit projects outward from the sidewall of the process container 4 and isopened on the other side to the interior of the process container 4. Inother words, the inner space of the gas exciting section 66 communicateswith the process field 5 within the process container 4. The opening 70has a vertical length sufficient to cover all the wafers W on the waferboat 12 in the vertical direction.

A pair of long and thin electrodes 74 are disposed on the opposite outersurfaces of the cover 72, and face each other in the longitudinaldirection (the vertical direction). The electrodes 74 are connected toan RF (Radio Frequency) power supply 76 for plasma generation, throughfeed lines 78. An RF voltage of, e.g., 13.56 MHz is applied to theelectrodes 74 to form an RF electric field for exciting plasma betweenthe electrodes 74. The frequency of the RF voltage is not limited to13.56 MHz, and it may be set at another frequency, e.g., 400 kHz.

The gas distribution nozzle 38 of the second process gas is bent outwardin the radial direction of the process container 4, at a position lowerthan the lowermost wafer W on the wafer boat 12. Then, the gasdistribution nozzle 38 vertically extends at the deepest position (thefarthest position from the center of the process container 4) in the gasexciting section 66. As shown also in FIG. 2, the gas distributionnozzle 38 is separated outward from an area sandwiched between the pairof electrodes 74 (a position where the RF electric field is mostintense), i.e., a plasma generation area PS where the main plasma isactually generated. The second process gas containing NH₃ gas is spoutedfrom the gas spouting holes 38A of the gas distribution nozzle 38 towardthe plasma generation area PS. Then, the second process gas isselectively excited (decomposed or activated) in the plasma generationarea PS, and is supplied in this state onto the wafers W on the waferboat 12.

An insulating protection cover 80 made of, e.g., quartz is attached onand covers the outer surface of the cover 72. A cooling mechanism (notshown) is disposed in the insulating protection cover 80 and comprisescoolant passages respectively facing the electrodes 74. The coolantpassages are supplied with a coolant, such as cooled nitrogen gas, tocool the electrodes 74. The insulating protection cover 80 is coveredwith a shield (not shown) disposed on the outer surface to prevent RFleakage.

At a position near and outside the opening 70 of the gas excitingsection 66, the gas distribution nozzle 40 of the first process gas isdisposed. Specifically, the gas distribution nozzle 40 extends upward onone side of the outside of the opening 70 (in the process container 4).The first process gas containing DCS gas is spouted from the gasspouting holes 40A of the gas distribution nozzle 40 toward the centerof the process container 4.

On the other hand, the exhaust port 68, which is formed opposite the gasexciting section 66, is covered with an exhaust port cover member 82.The exhaust port cover member 82 is made of quartz with a U-shapecross-section, and attached by welding. The exhaust cover member 82extends upward along the sidewall of the process container 4, and has agas outlet 84 at the top of the process container 4. The gas outlet 84is connected to a vacuum-exhaust system GE including a vacuum pump andso forth.

The process container 4 is surrounded by a heater 86, which is used forheating the atmosphere within the process container 4 and the wafers W.A thermocouple (not shown) is disposed near the exhaust port 68 in theprocess container 4 to control the heater 86.

The film formation apparatus 2 further includes a main control section60 formed of, e.g., a computer, to control the entire apparatus. Themain control section 60 can control the film formation process andpre-coating process described below in accordance with process recipesstored in the storage section 62 thereof in advance, with reference tothe film thickness and composition of a film to be formed. In thestorage section 62, the relationship between the process gas flow ratesand the thickness and composition of the film is also stored as controldata in advance. Accordingly, the main control section 60 can controlthe elevating mechanism 25, gas supply circuits 28, 30, and 36, exhaustsystem GE, gas exciting section 66, heater 86, and so forth, based onthe stored process recipes and control data. Examples of a storagemedium are a magnetic disk (flexible disk, hard disk (a representativeof which is a hard disk included in the storage section 62), etc.), anoptical disk (CD, DVD, etc.), a magneto-optical disk (MO, etc.), and asemiconductor memory.

Next, an explanation will be given of a film formation method (so calledALD or MLD film formation) performed in the apparatus shown in FIG. 1.In this film formation method, a silicon nitride film is formed onsemiconductor wafers by ALD or MLD. In order to achieve this, a firstprocess gas containing dichlorosilane (DCS) gas as a silane family gasand a second process gas containing ammonia (NH₃) gas as a nitriding gasare selectively supplied into the process field 5 accommodating wafersW. Specifically, a film formation process is performed along with thefollowing operations.

<Film Formation Process>

At first, the wafer boat 12 at room temperature, which supports a numberof, e.g., 50 to 100, wafers having a diameter of 300 mm, is loaded intothe process container 4 heated at a predetermined temperature, and theprocess container 4 is airtightly closed. Then, the interior of theprocess container 4 is vacuum-exhausted and kept at a predeterminedprocess pressure, and the wafer temperature is increased to a processtemperature for film formation. At this time, the apparatus is in awaiting state until the temperature becomes stable. Then, while thewafer boat 12 is rotated, the first and second process gases areintermittently supplied from the respective gas distribution nozzles 40and 38 at controlled flow rates.

The first process gas containing DCS gas is supplied from the gasspouting holes 40A of the gas distribution nozzle 40 to form gas flowsparallel with the wafers W on the wafer boat 12. While being supplied,the DCS gas is activated by the heating temperature to the process field5, and molecules of the DCS gas and molecules and atoms of decompositionproducts generated by decomposition are adsorbed on the wafers W.

On the other hand, the second process gas containing NH₃ gas is suppliedfrom the gas spouting holes 38A of the gas distribution nozzle 38 toform gas flows parallel with the wafers W on the wafer boat 12. When thesecond process gas is supplied, the gas exciting section 66 is set inthe ON-state or OFF-state, depending on the cycle sets, as describedlater.

When the gas exciting section 66 is set in the ON-state, the secondprocess gas is excited and partly turned into plasma when it passesthrough the plasma generation area PS between the pair of electrodes 74.At this time, for example, radicals (activated species), such as N*,NH*, NH₂*, and NH₃*, are produced (the symbol ┌*┘ denotes that it is aradical). On the other hand, when the gas exciting section 66 is set inthe OFF-state, the second process gas passes, mainly as gas molecules,through the gas exciting section 66. The radicals or gas molecules flowout from the opening 70 of the gas exciting section 66 toward the centerof the process container 4, and are supplied into gaps between thewafers W in a laminar flow state.

Radicals derived from the NH₃ gas excited by plasma or molecules of theNH₃ gas and molecules and atoms of decomposition products generated bydecomposition due to activation by the heating temperature to theprocess field 5 react with molecules and so forth of DCS gas adsorbed onthe surface of the wafers W, so that a thin film is formed on the wafersW. Alternatively, when the DCS gas flows onto radicals derived from theNH₃ gas or molecules and atoms of decomposition products derived fromthe NH₃ gas and adsorbed on the surface of the wafers W, the samereaction is caused, so a silicon nitride film is formed on the wafers W.When the gas exciting section 66 is set in the ON-state, the filmformation is developed at an increased reaction rate. On the other hand,when the gas exciting section 66 is set in the OFF-state, the filmformation is developed at a decreased reaction rate.

FIG. 3 is a timing chart showing the gas supply and RF (radio frequency)application of a film formation method according to an embodiment of thepresent invention. As shown in FIG. 3, the film formation methodaccording to this embodiment repeats a first cycle set SC1 and a secondcycle set SC2 mixedly, such as alternately as in this example, aplurality of times. The first cycle set SC1 is composed of a cycle orcycles in which the second process gas containing NH₃ gas is excited bythe gas exciting section 66. The second cycle set SC2 is composed of acycle or cycles in which the second process gas is not excited by thegas exciting section 66. Each of the first and second cycle sets SC1 andSC2 is formed of a set of three cycles, and each of the cycles is formedof first to fourth steps T1 to T4. Accordingly, a cycle comprising thefirst to fourth steps T1 to T4 is repeated a number of times, and thinfilms of silicon nitride formed by respective cycles are laminated,thereby arriving at a silicon nitride film having a target thickness.

Specifically, the first step T1 is arranged to perform supply of thefirst process gas (denoted as DCS in FIG. 3) to the process field 5,while maintaining the shut-off state of supply of the second process gas(denoted as NH₃ in FIG. 3) to the process field 5. The second step T2 isarranged to maintain the shut-off state of supply of the first andsecond process gases to the process field 5. The third step T3 isarranged to perform supply of the second process gas to the processfield 5, while maintaining the shut-off state of supply of the firstprocess gas to the process field 5. The fourth step T4 is arranged tomaintain the shut-off state of supply of the first and second processgases to the process field 5.

Each of the second and fourth steps T2 and T4 is used as a purge step toremove the residual gas within the process container 4. The term “purge”means removal of the residual gas within the process container 4 byvacuum-exhausting the interior of the process container 4 whilesupplying an inactive gas, such as N₂ gas, into the process container 4,or by vacuum-exhausting the interior of the process container 4 whilemaintaining the shut-off state of supply of all the gases. In thisrespect, the second and fourth steps T2 and T4 may be arranged such thatthe first half utilizes only vacuum-exhaust and the second half utilizesboth vacuum-exhaust and inactive gas supply. Further, the first andthird steps T1 and T3 may be arranged to stop vacuum-exhausting theprocess container 4 while supplying each of the first and second processgases. However, where supplying each of the first and second processgases is performed along with vacuum-exhausting the process container 4,the interior of the process container 4 can be continuouslyvacuum-exhausted over the entirety of the first to fourth steps T1 toT4.

In the third step T3 of the first cycle set SC1, the RF power supply 76is set in the ON-state to turn the second process gas into plasma by thegas exciting section 66, so as to supply the second process gas in anactivated state to the process field 5. In the third step T3 of thesecond cycle set SC2, the RF power supply 76 is set in the OFF-state notto turn the second process gas into plasma by the gas exciting section66, while supplying the second process gas to the process field 5.However, the heating temperature set by the heater 86 to the processfield 5 remains the same in the first and second cycle sets SC1 and SC2,i.e., it is essentially not changed depending on the cycle sets.

In FIG. 3, the first step T1 is set to be within a range of about 2 to10 seconds, the second step T2 is set to be within a range of about 5 to15 seconds, the third step T3 is set to be within a range of about 10 to20 seconds, and the fourth step T4 is set to be within a range of about5 to 15 seconds. As an average value provided by the first and secondcycle sets SC1 and SC2, the film thickness obtained by one cycle of thefirst to fourth steps T1 to T4 is about 0.11 to 0.13 nm. Accordingly,for example, where the target film thickness is 50 nm, the cycle isrepeated about 450 times (=150 cycle sets). However, these values oftime and thickness are merely examples and thus are not limiting.

FIG. 4 is a view showing a modification concerning the ON-state of an RFpower supply in the NH₃ gas supply step. In this modification, halfwaythrough the third step T3, the RF power supply 76 is set in the ON-stateto supply the second process gas in an activated state to the processfield 5 during a sub-step T3 b. Specifically, in the third step T3, theRF power supply 76 is turned on after a predetermined time Δt passes, toturn the second process gas into plasma by the gas exciting section 66,so as to supply the second process gas in an activated state to theprocess field 5 during the sub-step T3 b. The predetermined time Δt isdefined as the time necessary for stabilizing the flow rate of NH₃ gas,which is set at, e.g., about 5 seconds. Since the RF power supply isturned on to generate plasma after the flow rate of the second processgas is stabilized, the uniformity of radical concentration among thewafers W (uniformity in the vertical direction) is improved.

FIG. 5 is a sectional view showing the laminated state of a siliconnitride film formed by use of the timing chart shown in FIG. 3. As shownin FIG. 5, SiN regions 90A formed by use of no plasma and SiN regions90B formed by use of plasma are alternately laminated on the surface ofa wafer W. In the case of the timing chart shown in FIG. 3, each of theSiN regions 90A and 90B is formed of three unit thin films correspondingto three cycles.

Where the film formation method described above is used, particlegeneration is decreased to the minimum, and a silicon nitride filmthereby formed is provided with film quality, as a whole, equivalent tothat of a film formed by use of plasma in all the NH₃ gas supply steps.Specifically, it is possible to greatly decrease the dielectric constantof the deposited silicon nitride film, and to greatly improve theetching resistance of the film in dry etching. For example, even wherethe film formation temperature is set at, e.g., 550° C., which is lowerthan the conventional film formation temperature of, e.g., about 760°C., it is possible to decrease the etching rate of the film relative todilute hydrofluoric acid used in a cleaning process or etching processperformed on the surface of the film. As a result, the film is notexcessively etched by cleaning, and thus the cleaning process isperformed with high controllability in the film thickness. Further, thefilm can sufficiently serve as an etching stopper film or inter-levelinsulating film.

The process conditions of the film formation process are as follows. Theflow rate of DCS gas is set to be within a range of 50 to 2,000 sccm,e.g., at 1,000 sccm (1 slm). The flow rate of NH₃ gas is set to bewithin a range of 500 to 5,000 sccm, e.g., at 1,000 sccm. The processtemperature is lower than ordinary CVD processes, and is set to bewithin a range of 300 to 700° C., and preferably of 450 to 630° C. Ifthe process temperature is lower than 300° C., essentially no film isdeposited because hardly any reaction is caused. If the processtemperature is higher than 700° C., a low quality CVD film is deposited,and existing films, such as a metal film, suffer thermal damage. Thetemperature of the process field 5 may be changed to some extentdepending on the presence and absence of plasma in the first and secondcycle sets SC1 and SC2. However, the heating temperature set by theheater 86 to the process field 5 remains essentially the same in thefirst and second cycle sets SC1 and SC2.

The process pressure is set to be within a range of 13 Pa (0.1 Torr) to13,300 Pa (100 Torr), preferably of 40 Pa (0.3 Torr) to 266 Pa (2 Torr),and more preferably of 93 P (0.7 Torr) to 107 P (0.8 Torr). For example,the process pressure is set at 1 Torr during the first step (DCS supplystep) T1, and at 0.3 Torr during the third step (NH₃ supply step) T3. Ifthe process pressure is lower than 13 Pa, the film formation ratebecomes lower than the practical level. Where the process pressure doesnot exceed 13,300 Pa, the reaction mode on the wafers W is mainly of anadsorption reaction, and thus a high quality thin film can be stablydeposited at a high film formation rate, thereby attaining a goodresult. However, if the process pressure exceeds 13,300 Pa, the reactionmode is shifted from the adsorption reaction to a vapor-phase reaction,which then becomes prevailing on the wafers W. This is undesirable,because the inter-substrate uniformity and planar uniformity of the filmare deteriorated, and the number of particles due to the vapor-phasereaction suddenly increases.

The number of cycles constituting each of the first and second cyclesets SC1 and SC2 is not limited to three, and one cycle set may bedefined by, e.g., one to ten cycles. In FIG. 3, the second cycle set SC2is first performed, but the first cycle set SC1 may be first performed.In FIG. 3, DCS is first supplied in each cycle, but NH₃ gas may be firstsupplied alternatively. The mixture state of the first and second cyclesets SC1 and SC2 does not have to be completely constant, but may berandom. However, in light of controllability, this mixture state ispreferably set constant (alternate state).

The number of cycles constituting the first cycle set SC1 is preferablyset to be larger than the number of cycles constituting the second cycleset SC2. If the second cycle set SC2 utilizing no plasma has anexcessively large number of constituting cycles, or the second cycle setSC2 is performed with an excessively large frequency, the film qualityis deteriorated. In reverse, if these factors are excessively small,particle generation is rapidly increased. For example, the first cycleset SC1 utilizing plasma may be formed of three cycles, four cycles, ora larger number of cycles, while the second cycle set SC2 utilizing noplasma may be formed of only one cycle or two cycles.

FIGS. 11A and 11B are timing charts each showing the gas supply and RF(radio frequency) application of a film formation method according to amodification of the present invention. In the modification shown in FIG.11A, each of the first and second cycle sets SC1 and SC2 is formed ofone cycle, and the first and second cycle sets SC1 and SC2 arealternately performed. In the modification shown in FIG. 11B, the firstcycle set SC1 is formed of two cycles, the second cycle set SC2 isformed of one cycle, and the first and second cycle sets SC1 and SC2 arealternately performed.

<Experiment>

As present examples PE1, PE2, and PE3 according to the embodimentdescribed above and comparative examples CE1 and CE2, a silicon nitridefilm was formed in the apparatus shown in FIG. 1 by film formationmethods respectively using different combinations of cycle setsperformed with plasma and cycle sets performed without plasma, and thenthe film thus formed was examined. In this experiment, the processconditions described above were employed as the reference for the filmformation process, while the film formation temperature was set at 550°C. and the target film thickness was set at about 50 nm.

FIG. 6 is a diagram showing combinations of cycle sets performed withplasma and cycle sets performed without plasma, according to the presentexamples and comparative examples used in the experiment. In FIG. 6, ashaded zone represents a first cycle set SC1 utilizing plasma in thethird step (NH₃ supply step) T3, while a blank zone represents a secondcycle set SC2 utilizing no plasma in the third step (NH₃ supply step)T3. In this experiment, one cycle set was formed of one cycle.

As shown in FIG. 6, (A) the comparative example CE1 was arranged suchthat all the cycle sets were the first cycle set SC1 utilizing plasma.(B) The comparative example CE2 was arranged such that all the cyclesets were the second cycle set SC2 utilizing no plasma. (C) The presentexample PE1 was arranged such that the first cycle set SC1 utilizingplasma and the second cycle set SC2 utilizing no plasma were alternatelyperformed in the ratio of one to one. The flow chart shown in FIG. 3corresponds to the present example PE1, although the number of cyclesconstituting one cycle set is different. (D) The present example PE2 wasarranged such that the first cycle set SC1 utilizing plasma and thesecond cycle set SC2 utilizing no plasma were alternately performed inthe ratio of two to one. (E) The present example PE3 was arranged suchthat the first cycle set SC1 utilizing plasma and the second cycle setSC2 utilizing no plasma were alternately performed in the ratio of threeto one.

The number of generated particles per wafer was measured on each ofsilicon nitride films formed by the present examples and comparativeexamples shown in FIG. 6. In this experiment, the same film formationapparatus was used to sequentially perform film formation processes inaccordance with the comparative example CE1, comparative example CE2,present example PE1, present example PE2, and present example PE3, inthis order. The size of particles to be measured was set to fall withina range of 0.08 to 1.00 μm. Wafers placed at TOP (top), CTR (center),and BTM (bottom) of the wafer boat 12 were used as measurement wafers.

FIG. 7 is a graph showing particle generation, in association withsilicon nitride films formed by the present examples and comparativeexamples shown in FIG. 6. As shown in FIG. 7, the comparative exampleCE1 unfavorably rendered a lot of particle generation with the number ofparticles of 300 or more over the entire positions of the wafer boat.However, the comparative example CE1 provided the silicon nitride filmwith fairly good film quality. The comparative example CE2 rendered avery good result with the number of particles of about 10 to 20 over theentire positions of the wafer boat. However, the comparative example CE2did not provide the silicon nitride film with good film quality.

On the other hand, the present examples PE1 to PE3 rendered the numberof particles gradually increased with an increase in the ratio of use ofplasma in the third step (NH₃ supply step) T3. However, the number ofparticles was favorably still far lower than that of the comparativeexample CE1. Further, the present examples PE1 to PE3 provided thesilicon nitride film with relatively good film quality.

Then, the stress of silicon nitride films formed by the present examplesand comparative examples shown in FIG. 6 was measured. If this filmstress is larger, the silicon nitride film can be easily cracked andpeeled, so particle generation may be developed. Wafers placed at TOP(top) and BTM (bottom) of the wafer boat 12 were used as measurementwafers.

FIG. 8 is a graph showing the stress of silicon nitride films formed bythe present examples and comparative examples shown in FIG. 6. As shownin FIG. 8, the comparative example CE1 rendered a film stress of about0.621 GPa, which was far higher than those of the comparative exampleCE2 and present examples PE1 to PE3. It is thought that such a high filmstress of the comparative example CE1 was one of the causes that broughtabout a large number of generated particles in the comparative exampleCE1, as described with reference to FIG. 7.

The film stress was lowest in the comparative example CE, and graduallyincreased with an increase in the ratio of use of plasma in the thirdstep (NH₃ supply step) T3. However, the maximum was 0.404 GPa in thepresent example PE3, which was still far lower than that of thecomparative example CE1. It is thought that such a low film stress wasone of the causes that brought about a small number of generatedparticles in the comparative example CE2 and present examples PE1 toPE3, as described with reference to FIG. 7. Further, by adjusting theratio of use of plasma in the third step (NH₃ supply step) T3, the filmstress was controlled.

Then, silicon nitride films formed by the present examples andcomparative examples shown in FIG. 6 were examined in terms of the filmformation rate and the inter-substrate uniformity and planar uniformityof the film thickness. Wafers placed at TOP (top), CTR (center), and BTM(bottom) of the wafer boat 12 were used as measurement wafers.

FIG. 9 is a graph showing the film formation rate and theinter-substrate uniformity and planar uniformity of the film thickness,in association with silicon nitride films formed by the present examplesand comparative examples shown in FIG. 6. In FIG. 9, bars denote filmformation rates, lines provided with symbols “□” denote the planaruniformity of the film thickness, and points defined by symbols “⋄”denote the inter-substrate uniformity of the film thickness.

As shown in FIG. 9, the comparative example CE1 rendered a high filmformation rate of about 0.126 nm/cycle due to the presence of plasma.The comparative example CE2 rendered a low film formation rate of about0.089 nm/cycle due to the absence of plasma. On the other hand, thepresent examples PE1 to PE3 rendered film formation rates lower thanthat of the comparative example CE1 but favorably far higher than thatof the comparative example CE2. Specifically, the film formation rateswere gradually higher with an increase in the ratio of use of plasma inthe third step (NH₃ supply step) T3, such that the present example PE1resulted in about 0.111 nm/cycle, and the present example PE3 resultedin about 0.119 nm/cycle.

As regards the planar uniformity of the film thickness, it differeddepending on the positions TOP, CTR, and BTM, but the present examplesPE1 to PE3 brought about relatively good results with the same tendency,as compared to the comparative example CE2. As regards theinter-substrate uniformity of the film thickness, the comparativeexamples CE1 and CE2 showed values of less than ±2%, while the presentexamples PE1 to PE3 favorably showed values of less than +1%.

Then, the etching rate of silicon nitride films formed by the presentexamples and comparative examples shown in FIG. 6 was measured. As anetching liquid, 0.5% dilute hydrofluoric acid (0.5%-DHF) was used.Wafers placed at TOP (top), CTR (center), and BTM (bottom) of the waferboat 12 were used as measurement wafers, but only one wafer placed atCTR (center) was used in the comparative example CE1.

FIG. 10 is a graph showing the etching rate of silicon nitride filmsformed by the present examples and comparative examples shown in FIG. 6.As shown in FIG. 10, the comparative example CE2 rendered a relativelylarge etching rate of about 0.592 nm/min. On the other hand, the presentexamples PE1 to PE3 rendered etching rates of about 0.525 to 0.545nm/min, which were smaller than that of the comparative example CE2 andwere closer to 0.553 nm/min of the comparative example CE1 that providedthe film with high quality. Hence, it was confirmed that the presentexamples PE1 to PE3 brought about good characteristics with low etchingrates.

<Pre-Coating Process>

In the film formation method according to the embodiment of the presentinvention, before a silicon nitride film is formed on target substratesor product semiconductor wafers W by the film formation processdescribed above, a pre-coating process may be performed to form apre-coating film inside the process container 4. In the pre-coatingprocess, the wafer boat 12 set in an empty state with no wafers heldthereon, or a state with dummy wafers held thereon in place of productsemiconductor wafers W, is placed in the process field 5. As regards gassupply, the pre-coating process is arranged to repeat a number of timesa cycle comprising the first to fourth steps T1 to T4 shown in FIG. 3,as in the film formation process. Consequently, thin films of siliconnitride formed by respective cycles are laminated, thereby arriving at apre-coating film of silicon nitride having a target thickness.

Specifically, the first step T1 is arranged to perform supply of thefirst process gas (denoted as DCS in FIG. 3) into the process container4, while maintaining the shut-off state of supply of the second processgas (denoted as NH₃ in FIG. 3) into the process container 4. The secondstep T2 is arranged to maintain the shut-off state of supply of thefirst and second process gases into the process container 4. The thirdstep T3 is arranged to perform supply of the second process gas into theprocess container 4, while maintaining the shut-off state of supply ofthe first process gas into the process container 4. The fourth step T4is arranged to maintain the shut-off state of supply of the first andsecond process gases into the process container 4. Each of the secondand fourth steps T2 and T4 is used as a purge step to remove theresidual gas within the process container 4.

However, in the third step T3 of the pre-coating process, the RF powersupply 76 is always set in the OFF-state not to turn the second processgas into plasma by the gas exciting section 66, while supplying thesecond process gas into the process container 4. In other words, thesecond cycle set SC2 utilizing no plasma is repeated to form apre-coating film inside the process container 4. The other processconditions of the pre-coating process, such as the process pressure andprocess temperature, are set to be the same as the process conditions ofthe film formation process described above.

With the pre-coating process, the surface of components inside theprocess container 4, such as the inner wall of the process container 4and the wafer boat 12, are covered with a pre-coating film of siliconnitride formed by use of no plasma. After the pre-coating film isformed, the wafer boat 12 is unloaded from the process container 4.Then, product wafers W to be subjected to the film formation process aretransferred onto this wafer boat 12 within the loading area (not shown),and the film formation process is subsequently performed in the mannerdescribed above.

Where the pre-coating process described above is combined with the filmformation process, it is possible to minimize particle generation due toby-product films deposited on the inner surface of the process container4. Consequently, the film quality of a silicon nitride film formed onwafers W by the film formation process is further improved. It wasconfirmed that, even where only the first cycle set SC1 utilizing plasmawas repeated in the film formation process after the pre-coatingprocess, particle generation was decreased.

<Other Modifications>

In the embodiment described above, for example, the exciting section 66for generating plasma of the film formation apparatus 2 is integrallycombined with the process container 4. Alternatively, the excitingsection 66 may be separately disposed from the process container 4, soas to excite NH₃ gas outside the process container 4 (so called remoteplasma), and then supply the excited NH₃ gas into the process container4.

In the embodiment described above, for example, the first process gascontains DCS gas as a silane family gas. In this respect, the silanefamily gas may contain at least one gas selected from the groupconsisting of dichlorosilane (DCS), hexachlorodisilane (HCD), monosilane(SiH₄), disilane (Si₂Cl₆), hexamethyl-disilazane (HMDS),tetrachlorosilane (TCS), disilylamine (DSA), trisilylamine (TSA),bistertial-butylaminosilane (BTBAS), trimethylsilane (TMS),dimethylsilane (DMS), and monomethylamine (MMA).

In the embodiment described above, for example, the second process gascontains NH₃ gas as a nitriding gas. In this respect, the nitriding gasmay contain at least one gas selected from the group consisting ofammonia (NH₃), nitrogen (N₂), dinitrogen oxide (N₂O), and nitrogen oxide(NO).

In the embodiment described above, a silicon nitride film to be formedmay be provided with components, such as boron (B) and/or carbon (C). Inthis case, each cycle of the film formation process further comprises astep or steps of supplying a doping gas and/or a carbon hydride gas. Aboron-containing gas used for doping boron may contain at least one gasselected from the group consisting of BCl₃, B₂H₆, BF₃, and B(CH₃)₃. Acarbon hydride gas used for adding carbon may contain at least one gasselected from the group consisting of acetylene, ethylene, methane,ethane, propane, and butane.

A target substrate is not limited to a semiconductor wafer, and it maybe another substrate, such as an LCD substrate or glass substrate.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A film formation method for a semiconductor process for forming asilicon nitride film on a target substrate, in a process field inside aprocess container configured to be selectively supplied with a firstprocess gas containing a silane family gas and a second process gascontaining a nitriding gas, and communicating with an exciting mechanismfor exciting the second process gas to be supplied, the methodcomprising a film formation process arranged to perform a plurality ofcycles in the process field with the target substrate placed therein tolaminate thin films respectively formed by the cycles on the targetsubstrate, thereby forming a silicon nitride film with a predeterminedthickness, each of the cycles comprising: a first supply step ofperforming supply of the first process gas to the process field whilemaintaining a shut-off state of supply of the second process gas to theprocess field; and a second supply step of performing supply of thesecond process gas to the process field while maintaining a shut-offstate of supply of the first process gas to the process field, whereinthe method is arranged to repeat a first cycle set and a second cycleset mixedly a plurality of times without an essential change in aheating temperature set to the process field: the first cycle set beingcomposed of a cycle or cycles in which the second supply step comprisesan excitation period of supplying the second process gas to the processfield while exciting the second process gas by the exciting mechanism;and the second cycle set being composed of a cycle or cycles in whichthe second supply step comprises no period of exciting the secondprocess gas by the exciting mechanism.
 2. The method according to claim1, wherein the method is arranged to repeat the first cycle set and thesecond cycle set alternately a plurality of times.
 3. The methodaccording to claim 1, wherein the first cycle set is formed of aplurality of cycles.
 4. The method according to claim 3, wherein thenumber of cycles forming the first cycle set is larger than the numberof cycles forming the second cycle set.
 5. The method according to claim1, wherein each of the cycles further comprises first and secondintermediate steps of exhausting gas from the process field whilemaintaining a shut-off state of supply of the first and second processgases to the process field, between the first and second supply stepsand after the second supply step, respectively.
 6. The method accordingto claim 5, wherein each of the cycles is arranged to continuouslyexhaust gas from the process field through the first supply step, thefirst intermediate step, the second supply step, and the secondintermediate step.
 7. The method according to claim 5, wherein each ofthe first and second intermediate steps comprises a period of supplyinga purge gas to the process field.
 8. The method according to claim 1,wherein the second supply step of the first cycle set further comprisesa period of supplying the second process gas to the process field whilenot exciting the second process gas by the exciting mechanism, beforethe excitation period.
 9. The method according to claim 1, wherein,before forming the silicon nitride film on the target substrate, themethod further comprises a pre-coating process arranged to perform aplurality of pre-cycles in the process container with no targetsubstrate placed therein to form a pre-coating film inside the processcontainer, each of the pre-cycles comprising: a first pre-step ofperforming supply of the first process gas into the process containerwhile maintaining a shut-off state of supply of the second process gasinto the process container; and a second pre-step of performing supplyof the second process gas into the process container while maintaining ashut-off state of supply of the first process gas into the processcontainer, wherein the second pre-step comprises no period of excitingthe second process gas by the exciting mechanism.
 10. The methodaccording to claim 9, wherein the pre-coating process is executed whilea support member for supporting the target substrate is set in an emptystate or in a state with a dummy substrate supported thereon in place ofthe target substrate and is placed in the process field.
 11. The methodaccording to claim 9, wherein each of the pre-cycles further comprisessteps of exhausting gas from the process container while maintaining ashut-off state of supply of the first and second process gases into theprocess container, between the first and second pre-steps and after thesecond pre-step, respectively.
 12. The method according to claim 1,wherein the first and second supply steps are arranged to set theprocess field at a temperature of 300 to 700° C.
 13. The methodaccording to claim 1, wherein the first and second supply steps arearranged to set the process field at a pressure of 13 Pa (0.1 Torr) to13,300 Pa (100 Torr).
 14. The method according to claim 1, wherein thesilane family gas contains at least one gas selected from the groupconsisting of dichlorosilane, hexachlorodisilane, monosilane, disilane,hexamethyldisilazane, tetrachlorosilane, disilylamine, trisilylamine,and bistertialbutylaminosilane, trimethylsilane, dimethylsilane, andmonomethylamine, and the nitriding gas contains at least one gasselected from the group consisting of ammonia, nitrogen, dinitrogenoxide, and nitrogen oxide.
 15. The method according to claim 14, whereineach of the cycles of the film formation process further comprises astep or steps of supplying at least one gas selected from the groupconsisting of a doping gas and a carbon hydride gas.
 16. The methodaccording to claim 1, wherein the process field is configured toaccommodate a plurality of target substrates supported at intervals in avertical direction on a support member.
 17. A film formation apparatusfor a semiconductor process, comprising: a process container having aprocess field configured to accommodate a target substrate; a supportmember configured to support the target substrate inside the processfield; a heater configured to heat the target substrate inside theprocess field; an exhaust system configured to exhaust gas from theprocess field; a first process gas supply circuit configured to supply afirst process gas containing a silane family gas to the process field; asecond process gas supply circuit configured to supply a second processgas containing a nitriding gas to the process field; an excitingmechanism configured to excite the second process gas to be supplied;and a control section configured to control an operation of theapparatus, wherein the control section is preset to execute a filmformation method for a semiconductor process for forming a siliconnitride film on the target substrate, the method comprising a filmformation process arranged to perform a plurality of cycles in theprocess field with the target substrate placed therein to laminate thinfilms respectively formed by the cycles on the target substrate, therebyforming a silicon nitride film with a predetermined thickness, each ofthe cycles comprising: a first supply step of performing supply of thefirst process gas to the process field while maintaining a shut-offstate of supply of the second process gas to the process field; and asecond supply step of performing supply of the second process gas to theprocess field while maintaining a shut-off state of supply of the firstprocess gas to the process field, wherein the method is arranged torepeat a first cycle set and a second cycle set mixedly a plurality oftimes without an essential change in a heating temperature set to theprocess field: the first cycle set being composed of a cycle or cyclesin which the second supply step comprises an excitation period ofsupplying the second process gas to the process field while exciting thesecond process gas by the exciting mechanism; and the second cycle setbeing composed of a cycle or cycles in which the second supply stepcomprises no period of exciting the second process gas by the excitingmechanism.
 18. The apparatus according to claim 17, wherein, beforeforming the silicon nitride film on the target substrate, the filmformation method executed by the control section further comprises apre-coating process arranged to perform a plurality of pre-cycles in theprocess container with no target substrate placed therein to form apre-coating film inside the process container, each of the pre-cyclescomprising: a first pre-step of performing supply of the first processgas into the process container while maintaining a shut-off state ofsupply of the second process gas into the process container; and asecond pre-step of performing supply of the second process gas into theprocess container while maintaining a shut-off state of supply of thefirst process gas into the process container, wherein the secondpre-step comprises no period of exciting the second process gas by theexciting mechanism.
 19. A computer readable medium containing programinstructions for execution on a processor, which is used for a filmformation apparatus for a semiconductor process for forming a siliconnitride film on a target substrate, in a process field inside a processcontainer configured to be selectively supplied with a first process gascontaining a silane family gas and a second process gas containing anitriding gas, and communicating with an exciting mechanism for excitingthe second process gas to be supplied, wherein the program instructions,when executed by the processor, cause the film formation apparatus toconduct a film formation method comprising a film formation processarranged to perform a plurality of cycles in the process field with thetarget substrate placed therein to laminate thin films respectivelyformed by the cycles on the target substrate, thereby forming a siliconnitride film with a predetermined thickness, each of the cyclescomprising: a first supply step of performing supply of the firstprocess gas to the process field while maintaining a shut-off state ofsupply of the second process gas to the process field; and a secondsupply step of performing supply of the second process gas to theprocess field while maintaining a shut-off state of supply of the firstprocess gas to the process field, wherein the method is arranged torepeat a first cycle set and a second cycle set mixedly a plurality oftimes without an essential change in a heating temperature set to theprocess field: the first cycle set being composed of a cycle or cyclesin which the second supply step comprises an excitation period ofsupplying the second process gas to the process field while exciting thesecond process gas by the exciting mechanism; and the second cycle setbeing composed of a cycle or cycles in which the second supply stepcomprises no period of exciting the second process gas by the excitingmechanism.
 20. The medium according to claim 19, wherein, before formingthe silicon nitride film on the target substrate, the film formationmethod executed in accordance with program instructions furthercomprises a pre-coating process arranged to perform a plurality ofpre-cycles in the process container with no target substrate placedtherein to form a pre-coating film inside the process container, each ofthe pre-cycles comprising: a first pre-step of performing supply of thefirst process gas into the process container while maintaining ashut-off state of supply of the second process gas into the processcontainer; and a second pre-step of performing supply of the secondprocess gas into the process container while maintaining a shut-offstate of supply of the first process gas into the process container,wherein the second pre-step comprises no period of exciting the secondprocess gas by the exciting mechanism.